Surface Flaws Research Articles

Cyclic contact fatigue behavior of baria-silicate glass-ceramics as a function of crystal aspect ratio

Ceramic materials are potentially useful for dental applications because of their esthetic potential and biocompatibility. However, evidence of contact fatigue damage in ceramics raises considerable concern regarding its effect on the survival probability predicted for dental prostheses. To simulate intraoral conditions, Hertzian indentation loading with steel indenters was applied in this study to characterize the fatigue failure mechanisms of ceramic materials. Baria silicate glasses and glass-ceramics with different aspect ratios of crystals were selected because the glass and crystal phases have similar density, elastic modulus, and thermal expansion coefficients. Therefore, this system is a model ceramic for studying the effect of crystal geometry on contact cyclic fatigue failure. The subsequent flexural strength results show that the failure of materials with a low fracture toughness such as baria-silicate glass (0.7 MPa m1/2) and glass-ceramic with an aspect ratio of 3.6/1 (1.3 MPa m1/2) initiated from cone cracks developed during cyclic loading for 103 to 105 cycles. The mean strengths of baria-silicate glass and glass-ceramics with an aspect ratio of 3.6/1 decreased significantly as a result of the presence of a cone crack. Failures of baria-silicate glass-ceramics with an aspect ratio of 8.1/1 (Kc = 2.1 MPa m1/2) were initiated from surface flaws caused by either grinding or cyclic loading. The gradual decrease of fracture stress was observed in specimens with an aspect ratio of 8.1/1 after loading in air for 103 to 105 cycles. A reduction of approximately 50 % in fracture stress levels was found for specimens with an aspect ratio of 8.1/1 after loading for 105 cycles in deionized water. Thus, even though this glass-ceramic with an 8.1/1 crystal aspect ratio material is tougher than that with a 3.6/1 crystal aspect ratio, the fatigue damage induced by a large number of cycles is comparable. The mechanisms for cyclic fatigue crack propagation in baria-silicate glass-ceramics are similar to those observed under quasi-static loading conditions. An intergranular fracture path was observed in glass-ceramics with an aspect ratio of 3.6/1. For an aspect ratio of 8.1/1, a transgranular fracture mode was dominant.

Contrast of color-changing metallic glasses reveals the glass properties beneath the surface

Recently, color-changing glasses have been developed from a series of Ce-based metallic alloys. The functionality originates from fast and spontaneous surface oxidation. In most cases, single-color glasses have been obtained, but in a few cases, multicolor glasses that have spatially-dependent color contrast have been found. The natural color contrast mostly results from the interference effects on the oxide layer. The present work investigates factors that influence and control the variable oxidation rate observed at different locations on the surface, and what manufacturing steps and processing history lead to the rate variation. It is found that cooling rate, residual strain, and precipitation in melt-spun ribbons are the effects controlling the oxidation rate giving the enhanced color contrast. Therefore, the final surface color contrast reflects the non-uniform distribution of enthalpy (glassy state), microstructure, and chemistry of the metallic glass beneath the surface. The inspection of natural color contrast also represents technologically useful method for early surface flaw detection in color-changing metallic glasses.

Driving mode analysis of quarter-elliptical flaw under cyclic loading

The operations of large moving systems are often compromised under high-speed and heavy duty conditions owing to the fatigue deterioration caused by surface flaws. In this context, the present research examines a novel computational model to explore the stability of stress raisers such as quarter-elliptical cracks and semi-elliptical cracks. The influences of crack-tip interactions and stress ratio effects on driving mode progression are analyzed through a damage tolerance-based analytical strategy.

Review and synthesis of stress intensity factor (SIF) solutions for elliptical surface cracks in round bars under tension loading: A Tribute to Leonardo Torres-Quevedo

In this paper different stress intensity factor (SIF) solutions numerically obtained by previous research on transversely cracked cylinders (round bars) subjected to tension loading are analyzed. Surface cracks or flaws are assumed to be semi-elliptical, and solutions are compared in the matter of SIF values at the center of the crack front and at the external surface of the cylinder, so that a wide range of crack aspect ratios and relative crack depths are studied, in order to provide the engineer with solutions applicable to different real situations in fracture mechanics or damage tolerance analyses such as static or cyclic (fatigue) loading, environmentally assisted cracking or corrosion-fatigue.In Memoriam: The paper is dedicated to the memory of the Spanish civil engineer Leonardo Torres-Quevedo.

Surface Defect Detection of Industrial Parts Based on YOLOv5

Industrial product quality inspection, a crucial procedure in industrial production, is crucial in assuring product yield. Product safety and quality inspections on industrial assembly lines are predominantly manual, and there is currently a dearth of safe and dependable inspection techniques. An improved surface defect detection approach based on YOLOv5 is proposed for the problem of surface flaws in industrial components in order to improve the quality detection effect of industrial production parts. To improve the effect of dense object detection, the image features are extracted by the convolutional network and enhanced by coordinate attention. BiFPN is utilized to fuse multi-scale features in order to lower the rate of missed detection and false detection for small target samples. The detectors from the Transformer structure are added to the complex problem of fine-grained detection to improve the predictability of challenging occurrences. According to the experimental findings, on the dataset for industrial parts defects, the proposed network increases the recall of the original algorithm in abnormal classes by 5.3%, reaching 91.6%. Its inference speed can approach 95FPS, indicating an improved real-time detection performance.

Fatigue degradation analysis of elliptical corner damage

Modern trends in failure prevention of large moving systems require understanding of surface flaw phenomena caused by complex loads. Thus, through this research work, a novel computational framework is designed to assess real-time dynamic responses of surface stress raisers. Analytical outcomes generated through the stress intensity analysis and fatigue life evaluations have clearly confirmed the application of the developed design framework as a sustainable strategy for achieving reliable bearing capacity of dynamically loaded systems.

Stress intensity factors in the specimen with a surface semi-elliptical defect

In this work, equations for stress intensity factors calculating in the specimen with a surface semi-elliptical defect in order to interpret experimental data of the surface crack growth rate tests at elevated temperatures were obtained. In the commercial finite element code ANSYS 3D finite element models with surface flaws for the range of the relative crack depth b/t = 0.1…0.7 and the aspect ratio b/a = 0.3…1 were generated. For these ratios stress intensity factors were calculated based on the finite element method. For the same configurations of semi-elliptical crack fronts using Murakami's stress intensity factors handbook stress intensity factors were calculated. It has been established that the results of numerical calculations and the Murakami's handbook have a similar pattern of the stress intensity factors distribution. For the stress intensity factors calculating in the specimen with a surface semi-elliptical crack to the Murakami's handbook specimen geometry-dependent stress intensity factor functions a correction function was added. The results allow to interpret the experimental data of the surface crack growth rate tests of the specimen at elevated temperatures.

Effect of Graphene Fillers on the Water Absorption and Mechanical Properties of NaOH‐Treated Kenaf Fiber‐Reinforced Epoxy Composites

This paper is focused on developing composites using kenaf fibers, epoxy polymer, and incorporation of graphene fillers. The kenaf fibers are treated with 5% NaOH to remove the hydrophilic nature and reinforced it with the hydrophobic matrix. The composites are fabricated using the compression moulding technique by keeping 60 wt.% epoxy as constant, and the graphene and kenaf fiber weights are changed accordingly. The samples for tensile, flexural, impact, hardness, and water absorption tests are prepared as per the ASTM D3039, D790, D256, D2240, and D572 standards, respectively. The effect of graphene fillers in the 5% NaOH‐treated kenaf fibers reinforced with the epoxy matrix is tested. Among the various samples, sample 4 which has 6% graphene addition in the epoxy matrix reinforced with 5% treated kenaf fiber displayed the highest tensile strength of 63 MPa, flexural strength of 97 MPa, impact strength of 9.56 kJ/m2, hardness value of 97, and lower water absorption of 5.13%. This is due to the proper dispersion of graphene fillers in the matrix which caused better interfacial adhesion between the fiber and matrix. The water absorption test showed the lowest value in sample S5 as the graphene fillers obstruct water penetration in the fibers. SEM analysis is done on the prepared samples to study the surface flaws and structural changes.

Non-destructive Testing and Geophysical Exploration

It is important to evaluate materials' strength and damage state in material mechanics. A series of inspection techniques called non-destructive testing is used to examine the state of such materials non-destructively. Non-destructive testing is an inspection technique that examines harmful damage to the interior or surface of an object without destroying the object. It can be broadly classified into methods to detect internal flaws by injecting radiation or ultrasonic waves into the object and methods to detect surface flaws by passing an electric current or magnetic flux near the surface. Non-invasive inspection is a method similar to non-destructive testing—however, non-invasive inspection targets humans, not objects. Non-destructive testing is used for our safety and security, and non-invasive testing is used for our health. Although non-destructive testing and non-invasive inspection are not directly related to geophysical exploration, they share many of the same underlying principles. Geophysical exploration targets subsurface structures, including underground resources such as oil, natural gas, and metal deposits, and is used for our wealth and comfort. Geophysical exploration can be thought of as an inspection technology for the subsurface. In this paper, geophysical exploration for the exploration of subsurface structures and resources is reviewed, and its relevance to nondestructive testing for material mechanics is explained. This paper provides an overview of non-destructive testing and geophysical exploration concerning the mechanics of materials. While non-destructive testing focuses only on flaws within a material, geophysical exploration focuses on the physical properties of the material as a whole, which may be useful for investigating material heterogeneity. I hope this paper has stimulated your interest in non-destructive testing and geophysical exploration.

An Overview of Tempered Glass Load Bearing Capability and Mechanical Behavior

The study explores if tempered or strengthened with wire meshes, a single glass layer can be termed protective glass. Tempered glass demolishes into small fragments with harsh corners when it fractures. Because of the fracture pattern (fractures in pieces), heat- or chemically pre-stressed glass panel cannot be called safety glass panel until laminated. Bending experiments were run, and the bending strength of single-layer tempered and float glass panel was calculated using well-known formulae. In the context of float and tempered glass panel, the computed values for surface complexation using ultimate strain were matched to the bending strength findings. The following question arises: are the strains measured in the centre of the glass and towards the edge comparable? Strain measurements were also taken on the surface of packed samples in the centre and towards the edge of the glass. Fractures with tiny sharp points characterize glass errors. Despite careful manufacturing and maintenance of glass panes, hits by sharp particles or environmental effects can produce surface flaws. Glass manufacturing processes, such as edge polishing, have an impact on glass strength and can produce defects that spread during the glass’s lifespan.

Investigation for Stress Intensity Factor Solutions on Nozzle Corner Flaw (Part 2)

In order to provide a stress intensity factor (K)-solution for a nozzle corner flaw subjected to internal pressure for the Japan Society of Mechanical Engineers (JSME) Rules on Fitness for Service (FFS) for nuclear power plant, four candidates, which are the Paris and Sih based solution, the Fife’s solution, the Kobayashi’s solution and the solution of a flat plate with a semi-elliptical surface flaw in the JSME Rules on FFS, were compared with the Ks by Finite Element Method. As the result, the flat plate solution was confirmed to be the most adequate for K calculation of a nozzle corner flaw in the JSME Rules on FFS.

SiC, titanium, nickel, and ferric acid reinforcement materials to enhance mechanical properties in aluminium alloys: A critical review

The purpose of this review is for the examination of the impact of reinforcement particles on the microstructural properties and mechanical characteristics of aluminium alloys produced by friction stir processing (FSP). Reinforcement material filling methods will be explored to assess the amount at which grain refinement takes place. Comparison is done between the tool that is employed to produce the said composites as well as different reinforcement materials that have been studied and tested. Surface flaws and the major issues in friction stir procedures are porosity and reinforcement clusters. Solid-state FSP improves characteristics in MMCs by fine-tuning grain size and uniformly dispersing reinforcement. This review is focused on literatureapproaches for improving existing materials through friction stir processing. The properties of the improved material can be an answer to various industrial needs. This paper presents a review of recent models for microstructural change in alloys through the FSP process. The effectiveness of the present techniques will be highlighted to show their adequacies andinadequacies in the study to propose new ways for future material advancements.

Design against Fatigue of Super Duplex Stainless Steel Structures Fabricated by Wire Arc Additive Manufacturing Process

Additive manufacturing (AM) is increasingly used to make complex components for a wide spectrum of applications in engineering, medicine and dentistry. Wire arc additive manufacturing (WAAM), as one of AM processes, utilises electric arc and metal wire to fabricate fully dense and heavy metal parts at relatively low costs and high-energy efficiencies. WAAM was successfully applied in the production of several welding-based metal structures. Recently, there was a growing interest in WAAM processing of super duplex stainless steels (SDSS) due to their high strength and excellent corrosion resistance, which make them the prime choice for load-bearing structures in marine applications. Although a number of studies investigated the microstructural and mechanical properties of WAAM-processed SDSS components, little is known regarding their fatigue performance, which is critical in engineering design. This study reports on the outcomes of fatigue tests and fracture surface fractography of WAAM-processed SDSS. The results obtained indicate a significant anisotropy of fatigue properties and fatigue crack initiations resulting from internal defects rather than surface flaws. Based on these experimental results, we suggest an effective design methodology to improve the fatigue life of the WAAM-fabricated SDSS components. We also indicate that post-manufacturing surface treatments should not be underlined for the enhanced fatigue resistance of WAAM-processed SDSS structures.

Experimental investigations on the fracture strength of soda‐lime silica glass at elevated temperatures

The surface strength of glass plays a significant role when dimensioning glass components in structural facades. Commonly soda‐lime silica glass is used as material in architectural glass design. Different environmental conditions for example the load rate, relative humidity, surface flaws etc., but also the ambient temperature can have a strong influence on the resulting surface strength. The relationship between temperature, especially elevated temperatures, and surface strength of soda‐lime silica glass has so far been rarely investigated. Therefore, this paper methodically presents an experimental test setup for the determination of bending strength at elevated temperatures as well as first results. To determine the bending tensile strength of soda‐lime silica glass as float glass, the double ring bending test was conducted on specimens with small test surfaces according to EN 1288‐5. The double ring bending tests were performed using a tensile fatigue testing machine with furnace on circular glass plates of soda‐lime silica glass in a temperature range from room temperature to 550 °C. Before testing, the specimens were first pre‐damaged (inducing crack with diamond), stored and heat treated as the final pre‐treatment step. To determine the load rate for the experiments at elevated temperatures, the experiment was simulated in advance for the various temperatures using the finite element method with consideration of structural relaxation. To account for the structural relaxation, the Narayanaswamy model was utilized.

Evaluation of 3D deformation field in siltstone with a pre-existing 3D surface flaw under uniaxial compression using X-ray computed tomography and digital volumetric speckle photography

The interior deformation or rupture of materials is usually derived from measuring the surface deformation of specimens. In this study, a set of uniaxial compression tests combined with in situ X-ray computed tomography (CT) was performed on siltstone specimens with a pre- existing three-dimensional (3D) surface flaw with various inclination angles (α = 30◦, 45◦, 60◦). The ratio of flaw depth to specimen thickness was 0.26. Based on the CT images of the specimens under different loads, the digital volumetric speckle photography procedure was applied to quantifying the 3D interior deformation of the specimens, and 3D displacement and major principal strain ε1 distribution in different sections were determined. The characteristics of internal strain before specimen fracturing indicated strain localization, which could describe the propagation mechanism of the single 3D surface flaw.

Effect of chemical strengthening residual stress on the flexural performance and fracture behavior of aluminosilicate glass

In this hybrid experimental, theoretical and numerical study the effect of chemical strengthening residual stress on the flexural strength and fracture behavior of aluminosilicate glass was investigated. Three-point bending tests were conducted on annealed and chemically strengthened glass specimens to obtain the flexural strength of both specimens and with the aid of high-speed cameras, the fracture and failure modes of these two kinds of specimens were analyzed and compared. A theoretical analysis based on the elastic fracture mechanics theory was employed to explain the strengthening effect of chemically strengthened glass. It is shown that the mechanical strength of chemically strengthened glass is highly related to the relation of the chemically strengthened layer depth and the surface flaw depth. Furthermore, this study provides an effective numerical approach to replicate the mechanical strength and failure modes for both annealed and chemically strengthened glass. The proposed finite element numerical method includes modeling techniques which consider the presence of pre-stress, random distributed surface flaws and the fracture onset in glass specimens. The residual stress pattern was defined exploiting the dynamic relaxation process for temperature-induced expansion of the elements before the loading process. Discrete distributed surface flaws were inserted in the model, the brittle fracture of glass was represented by the smeared crack method and the numerical results were compared to experimental data. It’s illustrated that the proposed method can be used to represent both the discrete fracture behavior and the chemically-strengthening effect of silicate glass.

An Investigation of Chemo-Mechanical Phenomena in All-Solid-State Lithium Metal Batteries Using in-Situ Curvature Measurements

Lithium metal penetration through garnet based LLZO solid electrolytes (SEs) have been identified as a critical failure process. At critical current density (CCD), LLZO SE has been known to short-circuiting, and can even result in fracturing of the SE. The combined chemo-mechanical phenomena- which can significantly affect the performance in all solid-state batteries, requires detailed investigation of several related phenomena. Characterizing the dynamical mechanical evolution that occurs in the electrode-SE is challenging. Investigation of the mechanical driving forces of lithium metal penetration through the SE is a particularly important challenge. To probe the chemo-mechanical phenomena that occur during lithium plating, this study reports in-situ curvature measurements that were designed to evaluate the stresses that evolve in LLZO during lithium plating. The experimental configuration created for this work provides data which was analyzed with a detailed Finite Element Model (FEM) to quantitatively evaluate stress evolution in the solid electrolyte. The results show that Li metal plating within a surface flaw can produce stress build-up prior to short-circuiting. The combined results from both the experiments and the FEM suggest that it is critical to minimize surface defects and flaws during manufacturing processes.

Study on the biological behaviors of Ca[sbnd]P coatings with different morphology on carbon/carbon composites

In this work, we designed and fabricated a CaP composite bio-coating with different surface morphologies on a carbon/carbon (C/C) matrix by means of hybrid supersonic atmospheric plasma spraying (SAPS) and microwave-hydrothermal (MH) technologies. We found that all studied coating materials can support mesenchymal stem cells (MSCs) proliferation with prolonged culture time (3 days and 7 days) in vitro. Furthermore, according to the (Confocal Laser Scanning Microscopy) CLSM results, the MSCs also showed good attachment and different spreading morphologies on SAPS/MH coatings. As such, C/C matrix, the MH treated coatings with needle-like and rod-like microstructures were chosen for further in vivo investigation. Considering the good bonding between host tissue and the studied materials, the in vivo morphology studies confirmed a good histocompatibility for all coating samples, as well as a decreasing expression for inflammatory factors in a physiological environment. The histological results around the implants indicated different cell aggregation and vascularization ability in the local micro-environment. In particular, based on the reduction of the C/C initial surface flaws (e.g. hydrophobicity, biological inertia and easily producing carbon fragments or particles), the MH treated coating with rod-like surface morphology with a specific surface area (~2.33 m2/g) and roughness (~13.80 μm), showed excellent performance as a promising implant in live tissue.

Effectively inhibiting particles aggregation and sedimentation for TiO2-H2O suspension by application of an electrode

Inhibiting particles aggregation plays a crucial role in maintaining the stability of nanofluids. In this work, applying a rod electrode was developed to reduce particles aggregation and sedimentation for TiO2-H2O suspensions. The experimental results show that the aggregation and sedimentation of TiO2 particles are effectively suppressed when a rod electrode is inserted into the TiO2-H2O suspensions due to the increase of the absolute value of particle zeta potential. There is an optimal electric voltage (0.5 kV) to achieve the maximum suppression of sedimentation, while surface flaw of the electrode is harmful to suppress sedimentation. The mechanism for inhibition of sedimentation by the electrode is speculated that the charges transfer between the electrode and the TiO2 nanoparticles by the contact electrification. Therefore, the application of the electrode with the optimal design has great potential for improving the stability of the TiO2-H2O nanofluids.

Numerical fracture mechanics as a practical failure investigatory tool: The outlook of cracked round bars

Many failure investigations related to the failed round bars/shafts for various applications have been reported in literature. The cracks were often initiated at the regions with a high stress concentration. However, numerical fracture mechanics was frequently not used in the failure investigations. Nowadays advancement of computational development on the interactive numerical techniques allows the analysts to more accessibly figure out the fracture phenomena when performing engineering analyses. In addition, the computational cost is no longer the issue of performing numerical fracture mechanics analyses. The stress intensity factors (SIFs) of a surface planar flaw at a stepped round bar are of practical interest, however, the SIF solutions along the flaw front were not yet documented in literature. Here, the practical abilities of the numerical fracture mechanics on the fracture analyses are demonstrated by evaluating a planar surface flaw at the shoulder fillet through numerical simulations by the finite element method (FEM) and the dual boundary element method (DBEM). The use of tetrahedral meshing of FEM is presented, and the concern of corner point singularity on a surface planar flaw is highlighted. The stress contours around the front of planar flaws that are hardly acknowledged in literature are also presented. The SIF behaviors of the semi-elliptical planar flaws are discussed. The SIF data for relatively small crack sizes are valuable to be used for judging a condition of crack size whether or not it would grow to a critical size.